Recently, demands for optical communication are abruptly increased in concert with the development of information communication techniques. Accordingly, the demand for the optical cables is also tending to increase. ADSS (All-Dielectric Self-Supporting Cable) is one of aerial optical cables. This ADSS cable is designed to include 2 to 144 strips of optical fibers.
Main features of the ADSS cable are that it is a completely nonmetallic cable, and capable of self-supporting. In addition, high tensile strength and tracking resistance are possessed therein. Moreover, the ADSS cable may be installed using an existing pylon with a low construction cost, so the ADSS cable is expected to show increased demand in the future.
The ADSS cable generally includes a core having an optical fiber unit and positioned at the center, and a sheath for protecting the core. Since the ADSS cable should ensure a life for a long time (about 30 years), relevant mechanical performance of the cable such as tensile property and bending of the cable is essential. In order to improve the tensile property of the ADSS cable, a tensile member is respectively adopted between the core and the sheath.
Conventionally, a tensile member in which an Aramid yarn is stranded with keeping regular pitches is used in the aforementioned sheath. However, this conventional method shows a deteriorated tensile property in an axial direction of the cable due to the load dispersion in a radial direction according to the Wire Rope theory, rather than the linear member. In addition, the cable is extended due to its own weight after the optical cable is installed, thereby generating a torsion, which is a factor of performance deterioration.
However, despite such problems; the reason of stranding the Aramid yarn in the convention method is that it prevents structural instability of the cable caused by inclination of the Aramid yarn, which is apt to be generated in bending the cable.
As described above, the conventional method for manufacturing an optical cable arouses deterioration of the tensile property and torsion of the cable, thereby giving optical losses and exerting a bad influence upon the life of the cable. In order to solve these problems, an improved method is proposed to use SZ-stranding, namely doubly stranding the Aramid yarn in opposite directions with keeping the pitch as it is.
However, the SZ-stranding method requires to add a complex process in the optical cable manufacturing procedure, thereby arousing several problems, such as increase of a production cost and a weight of the cable. In addition, since this method cannot be applied to an optical cable having a small diameter, the Aramid yarn should be stranded in one direction in such an optical cable.